Although supported by a back-up team and divers, she swam without a protective shark cage, instead relying on an electronic shield, unnoticeable to humans, mounted on a kayak as a shark deterrent.

This marks her third attempt since last summer to become the first person to swim across the Straits of Florida without a shark cage.

In 1978 she also made a failed attempt, but with the protection of a shark cage.

Miss Nyad first attempted the Straits of Florida when she was 29. Sharks, jellyfish, and unexpectedly extreme weather left her swimming towards Texas rather than her destination in Florida and caused the swim to be abadoned.

During her second attempt she was forced to retire after acute shoulder pain and an 11 hour asthma attack following multiple jellyfish stings.

A renowned veteran swimmer, Miss Nyad has received accolades from around the world, with many supporting her most recent endeavour through Twitter.

Miss Nyad was one of the first women to swim around the island of Manhattan, breaking the then world record for the feat in 1975. She currently holds the world record for longest ocean swim – travelling 102.5 miles from the Bahamas to Jupiter in Florida.

In 2003 Miss Nyad was inducted into the American International Swimmers Hall of Fame.